Chandra Detects Record-Breaking X-Ray Jet

An international team of scientists using NASA’s Chandra X-ray Observatory has discovered a jet of X-rays from a supermassive black hole about 12.4 billion light years away, the most distant X-ray jet ever observed.

This is a composite image of the record-setting X-ray jet produced by the quasar GB 1428+4217 (X-ray: NASA / CXC / NRC / C.Cheung et al; optical: NASA / STScI; radio: NSF / NRAO / VLA)

According to the study published in the Astrophysical Journal Letters (arXiv.org version), this X-ray jet was produced by a quasar named GB 1428+4217 (GB 1428 for short).

Giant black holes at the centers of galaxies can pull in matter at a rapid rate producing the quasar phenomenon. The energy released as particles fall toward the black hole generates intense radiation and powerful beams of high-energy particles that blast away from the black hole at nearly the speed of light. These particle beams can interact with magnetic fields or ambient photons to produce jets of radiation.

“We’re excited about this result not just because it’s a record holder, but because very few X-ray jets are known in the early Universe,” said Dr Teddy Cheung of the National Academy of Sciences, lead author of the ApJ paper.

As the electrons in the jet fly away from the quasar, they move through a sea of background photons left behind after the Big Bang. When a fast-moving electron collides with one of these so-called cosmic microwave background photons, it can boost the photon’s energy into the X-ray band.

“Since the brightness of the jet in X-rays depends, among other things, on how fast the electrons are moving away from the black hole, discoveries like the jet in GB 1428 tell us something about the environment around supermassive black holes and their host galaxies not that long after the Big Bang,” said co-author Dr Lukasz Stawarz of the Japan Aerospace Exploration Agency in Kanagawa, Japan.

Because the quasar is seen when the Universe is at an age of about 1.3 billion years, less than 10% of its current value, the cosmic background radiation is a thousand times more intense than it is now. This makes the jet much brighter, and compensates in part for the dimming due to distance.

“We’re lucky that the Universe gives us this natural amplifier and lets us detect this object with relatively short exposures,” said co-author Dr Aneta Siemiginowska, of the Harvard-Smithsonian Center for Astrophysics in Cambridge. “Otherwise we might miss important physical processes happening at very large distances from Earth and as far away as GB 1428.”

While there is another possible source of X-rays for the jet – radiation from electrons spiraling around magnetic field lines in the jet – the scientists favor the idea that the cosmic background radiation is being boosted because the jet is so bright.

The researchers think the length of the jet in GB 1428 is at least 230,000 light years, or about twice the diameter of the entire Milky Way Galaxy.

Observations of GB 1428 with a set of radio telescopes at different locations around the Earth revealed the presence of a much smaller jet, about 1,900 light years long, which points in a similar direction to the X-ray jet.

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Bibliographic information: C. C. Cheung et al. 2012. Discovery of a Kiloparsec-scale X-Ray/Radio Jet in the z = 4.72 Quasar GB 1428+4217. ApJ 756, L20; doi: 10.1088/2041-8205/756/1/L20